3 Types of Rocks. On the bases of their formation, rocks are broadly divided into three types, namely igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are found in volcanic regions. Igneous rocks are formed from magma, which is a molten material found deep inside the earth. This molten magma comes upwards or even erupts from a volcano in the form of lava. When this lava cools, it leads to the formation of igneous rocks. Pumice and Granite are examples of igneous rocks. Sandstone, coal and limestone are examples of sedimentary rocks. When limestone is subjected to pressure and heat, it forms marble, a type of metamorphic rock. Quartzite and slate are examples of metamorphic rocks.